The existing chairs can be categorized as an office chair, a household chair and most of the multifunctional chairs. Apart from ensuring the strength and stability of the chair, the comfort level and the health of a human body are also emphasized while designing a chair. Particularly, as to the design of the backrest of the chair, the protection of the lumbar vertebra and the spine of the human body needs to be taken into consideration. Therefore, the chair backrest can be specially designed, for example, a motor transmission assembly is designed on the backrest chair frame, to allow the user to adjust the backrest according to the requirements of the user, so that the comfort level can be improved while the waist and the back of the human body can be protected.
Referring to the chair frame of the existing multifunctional chair shown in FIG. 1, which can be unfolded as a deck chair or a massage chair, and the multifunctional chair can also move upward and downward to work as a general office or household chair after being retracted. A plurality of use requirements can be met for people, and therefore, the multifunctional chair is preferred by a great number of users. The chair frame of the multifunctional chair generally includes a seat part, a backrest part and a pedal part which can be unfolded or retracted. Currently, a motor transmission mechanism is installed at the lower part of the chair frame of the seat part, so that the position of the backrest part can be adjusted by the action of backrest part.
According to the invention, the adjusting action of the backrest bracket 100 is realized by installing a motor transmission mechanism 10 at the bottom of the chair frame. The motor transmission mechanism 10 includes a fixing part 12 connected to a connecting plate 110 of the backrest bracket 100, a motor speed reducing module 14, a screw rod transmission module 15 connected to the speed reducing module 14, an ejector rod 16 connected to the screw rod transmission module 15, and a connecting structure 18 fixed to the chair frame component arranged at the end part of the ejector rod 16. According to the motor transmission mechanism, the screw rod transmission mechanism is used for driving the ejector rod 16 to reciprocate to achieve the movements of the chair frame related part. An installation space and a movement space of a long distance are required to guarantee the normal work of the motor transmission mechanism. In addition, the fixed part 12 at the top and the connecting plate 110, and the connecting structure 18 at the top end of the ejector rod 16 and the chair frame component, are both connected and fixed by adopting a rivet point connection mode. Hence, the stability of the movement of the backrest and the stability of the whole chair after adjusting the backrest are influenced, and the backrest is relatively easy to shake. Particularly, when the weight of a person on the chair is too large, the ejection rod of the motor transmission mechanism can be easily deformed due to frequent shaking. Therefore, it is necessary to provide a motor transmission mechanism which is simple in structure and higher in operation process and supporting stability. Meanwhile, the installation space of the chair also needs to be taken into consideration.